Mark used to be a Runaway in the world of the Railway where trains and passengers acted like thoughts in a brain. He discovered that the Railway was only one of many living transport systems. Now, he is an Apprentice to the Board of Transport, the organisation that controls them.
As part of his apprenticeship, Mark is given a work placement, watching negotiations in a border dispute between the Waterways and the Sea. The negotiations are being mediated by Helen, an old friend from the Railway.
A series of bombings and an assassination soon cause a routine dispute to start heading towards a full-blown war.
Caught between the two sides, will Mark be able to defuse the situation before it kills him?